Clutter Cloak is described as 'tiny anti-distraction program for Windows XP'. There are four alternatives to Clutter Cloak for Mac and Windows. The best alternative is HazeOver. It's not free, so if you're looking for a free alternative, you could try LeDimmer or Backdrop.
Too many windows to manage? Big display? Or getting lost in multiple monitors? HazeOver is for you! ? TRIAL version: HazeOver.com Get rid of distractions and focus on your current task. HazeOver automatically highlights the front app window by dimming all background windows.